Polyisocyanate used as a raw material of polyurethane is industrially produced by allowing carbonyl chloride to react with polyamine for isocyanate reaction.
In this isocyanate reaction, corresponding polyisocyanate is produced from polyamine and a large quantity of hydrochloric gas is produced secondarily.
The hydrochloric gas produced secondarily is used for oxychlorination in production of vinyl chloride, for example.
Further, a production method for producing chlorine industrially by oxidizing the hydrochloric gas produced secondarily has been proposed (cf. Patent Document 1 and Patent Document 2, for example).
When hydrochloric gas is oxidized, water is also produced secondarily together with chlorine. The mixture of chlorine and water thus produced is dehydrated using a sulfuric acid to dry the chlorine, as is known (cf. Patent Document 3, for example).
Patent Document 1: Japanese Unexamined Patent Publication No. 62-275001,
Patent Document 2: Japanese Unexamined Patent Publication No. 2000-272906, and
Patent Document 3: Japanese Unexamined Patent Publication No. 2004-217455.